This website hosts the TRB Standing Committee on Transit Data.
It's a clever way of managing code, and a website is just a bunch of code
While working on the website locally on your computer, it can be helpful to preview what your changes will look like before pushing them up to GitHub.
Assuming you already have Ruby installed, the short of it is:
bundle install
bundle exec jekyll serve
GitHub offers a more comprehensive guide if you have trouble with the above: Testing your Github Pages site locally with Jekyll